Transition metal doped germanium-antimony-tellurium (GST) memory device components and composition

ABSTRACT

Methods, systems, and devices for operating memory cell(s) using transition metal doped GST are described. As discussed herein, a composition including germanium (Ge), antimony (Sb), tellurium (Te), and at least one of yttrium (Y) and scandium (Sc) may be used as a memory element in a memory cell. For example, a memory element may include a composition having Ge in an amount ranging from 15 to 35 atomic percent (at. %) of the composition, Sb in an amount less than or equal to 50 at. % of the composition, Te in an amount greater than or equal to 40 at. % of the composition, and at least one of Y and Sc in an amount ranging from 0.15 to 10 at. % of the composition.

CROSS REFERENCE

The present Application for Patent claims priority to U.S. patentapplication Ser. No. 16/107,930 by Fantini et al., entitled “TRANSITIONMETAL DOPED GERMANIUM-ANTIMONY-TELLURIUM (GST) MEMORY DEVICE COMPONENTSAND COMPOSITION,” filed Aug. 21, 2018, which is assigned to the assigneehereof and is expressly incorporated by reference in its entirety.

BACKGROUND

The following relates generally to operating a memory array and morespecifically to transition metal doped germanium (Ge)-antimony(Sb)-tellurium (Te) (GST) and related memory devices.

Memory devices are widely used to store information in variouselectronic devices such as computers, wireless communication devices,cameras, digital displays, and the like. Information is stored byprograming different states of a memory device. For example, binarydevices have two states, often denoted by a logic “1” or a logic “0.” Inother systems, more than two states may be stored. To access the storedinformation, a component of the electronic device may read, or sense,the stored state in the memory device. To store information, a componentof the electronic device may write, or program, the state in the memorydevice.

Various types of memory devices exist, including magnetic hard disks,random access memory (RAM), read only memory (ROM), dynamic RAM (DRAM),synchronous dynamic RAM (SDRAM), ferroelectric RAM (FeRAM), magnetic RAM(MRAM), resistive RAM (RRAM), flash memory, phase change memory (PCM),and others. Memory devices may be volatile or non-volatile. Non-volatilememory (e.g., FeRAM, PCM, RRAM) may maintain their stored logic statefor extended periods of time even in the absence of an external powersource. Volatile memory devices (e.g., DRAM) may lose their stored stateover time unless they are periodically refreshed by an external powersource.

Chalcogenide material compositions may be used in components of a phasechange memory cell—e.g., in a selector device or memory element. Thesecomponents may have a first threshold voltage at which they becomeconductive (current is allowed to flow through the composition) when inan amorphous state and a different threshold voltage when in acrystalline state, and the difference between the first thresholdvoltage and the second threshold voltage may be referred to as thresholdvoltage window. In some cases, a sensing window of a phase change memorycell depends on the threshold voltage window of a correspondingchalcogenide material—e.g., a sensing window may increase as thethreshold voltage window of the chalcogenide material increases.However, memory components having larger threshold voltage windows mayin some cases also have slower crystallization (or SET) speeds (thespeed with which the composition transitions from an amorphous to acrystalline state), which may decrease the operational speed of acorresponding memory cell. Improved memory devices are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a memory array that supports transitionmetal doped germanium-antimony-tellurium (GST) in accordance withvarious aspects of the present disclosure.

FIG. 2 illustrates an example cross-section of a memory array thatsupports transition metal doped GST in accordance with various aspectsof the present disclosure.

FIG. 3 illustrates an example of a plot for transition metal doped GSTin accordance with various aspects of the present disclosure.

FIG. 4 illustrates an example ternary diagram showing example transitionmetal doped GST compositions in accordance with various aspects of thepresent disclosure.

FIG. 5 illustrates an example memory array that supports transitionmetal doped GST in accordance with various embodiments of the presentdisclosure.

FIG. 6 illustrates an example system that supports transition metaldoped GST and related memory devices in accordance with variousembodiments of the present disclosure.

FIG. 7 illustrates a flowchart of a method or methods for transitionmetal doped GST in accordance with various embodiments of the presentdisclosure.

DETAILED DESCRIPTION

Electronic data may be stored in memory cells containing memory elementsthat are electronically programmable (e.g., by way of applying a voltageor current) to have different resistivity (e.g., a resistance orthreshold voltage). For example, a logic value may be stored in a memorycell by changing a resistivity of a corresponding memory element, wherea first resistivity of the memory element corresponds to a first logicvalue and a second resistivity of the memory element corresponds to asecond logic value.

A memory element having an electronically programmable resistivity mayinclude a material that exhibits a different resistivity based on aphase of the material—e.g., based on whether the material is in anamorphous phase or a crystalline phase. One example of these materialsmay include or be referred to as phase change materials. In someexamples, a memory element containing a phase change material in a firstphase (e.g., the amorphous phase) may exhibit a first resistance and/orhave a first threshold voltage and the memory element containing thephase change material in a second phase (e.g., the crystalline phase)may exhibit a second resistance and/or have a second threshold voltage.In some cases, the first threshold voltage may be greater than thesecond threshold voltage and the difference between the first thresholdvoltage and the second threshold voltage may be referred to as thethreshold voltage window for the memory element.

The different programmable resistivity states of a memory element maydepend on physical characteristics of the memory element, such as acomposition of the phase change material included in the memory elementand a size of the memory element, among other factors. In some cases, athreshold voltage, and thus a threshold voltage window, of a memoryelement may be correlated with a bandgap of the phase changematerial—e.g., the threshold voltage window of the memory element mayincrease as the bandgap of the phase change material increases, and viceversa. A bandgap of a phase change material may be based on a molecularstructure of the phase change material. In some cases, a bandgap of thephase change material may be based on electronegativity of the differentelements.

Accordingly, certain phase change materials may have higher or lowerbandgaps based on a particular combination of elements making up thephase change material. For instance, a phase change material thatincludes indium (In), antimony (Sb), and tellurium (Te) (which may bereferred to as IST) or In, germanium (Ge), and Te (which may be referredto as IGT) may have a large bandgap, whereas a phase change materialthat includes only Ge, Sb, and Te (which may be referred to as GST) mayhave a narrow bandgap. The threshold voltage window of a memory elementmay also be correlated with a size of the memory element—e.g., thethreshold voltage window of a memory element may decrease as a size ofthe memory element decreases, and vice versa.

In some examples, a phase of a phase change material in a memory elementmay be changed to store a logic value at a corresponding memorycell—e.g., during a write operation. In some examples, a phase of aphase change material may be changed by applying one or more voltagesacross (or currents to—e.g., through) the phase change material, heatingthe material to at least a certain temperature (which may be referred toas the glass transition temperature or melting temperature) and coolingthe material (which may also be referred to as quenching) by removing oraltering the applied voltage or current so as to cause a phase of thephase change material to transition from one phase to another phase. Thedifferent phases of the phase change materials may correspond toparticular logic values. For example, when the phase change material isin the amorphous phase, a corresponding memory element/cell may store afirst logic value (e.g., have a first resistivity) and when the phasechange memory material is in the crystalline phase, the correspondingmemory element/cell may store a second logic value (e.g., have a secondresistivity).

The speed with which a memory element including a phase change materialtransitions from the amorphous to the crystalline phase may be referredto as a “SET speed” of the memory element, and the speed with which thememory element transitions from the crystalline phase to the amorphousphase may be referred to as a “RESET speed” of the memory element.Similarly, the time required for transitioning a phase change materialof a memory element from an amorphous to crystalline phase may bereferred to as a “SET duration” and the time required for transitioninga phase change material of a memory element from a crystalline toamorphous phase may be referred to as a “RESET duration.”

Like the threshold voltage window of a memory element, a SET speed of amemory element may be based on a molecular structure of a phase changematerial in the memory element. In some cases, the SET speed/durationmay be a function of the number of four-fold rings in a composition,which may act as nuclei for crystallization—e.g., a composition with alarge number of four-fold rings may have a faster SET speed/shorter SETduration than a composition with less four-fold rings. Accordingly,certain memory elements may have faster or slower SET speeds based on aparticular combination of elements making up the phase change materialsin a memory element.

In some cases, a SET speed of a memory element is inversely correlatedwith a bandgap of a phase change material in the memory element—e.g., asthe bandgap of a phase change material decreases, the SET speed of acorresponding memory element quickens, and vice versa. For instance,memory elements using phase change materials having compositions withlarge bandgaps, such as IST and IGT, may have slow SET speeds. Thisrelationship occurs because the addition of elements that increase abandgap of a phase change material also typically reduces the number offour-fold rings in the phase change material.

In some examples, a phase of a phase change material in a memory elementmay be used to determine a logic value stored at a corresponding memorycell—e.g., during a read operation to provide requested data to arequesting device (e.g., a memory component or external device). Forexample, a logic value stored in a memory cell may be determined bysensing a resistivity of a memory element contained in the memory cell.Among other techniques, the resistivity of the storage element may besensed by applying a voltage to a memory cell and determining whether,or how much, current flows through the memory cell. In such cases, thelarger the difference in resistivity of the memory element betweendifferent phases, the more reliably (e.g., with lower error rates) thelogic values stored at the memory cell may be determined (e.g., sensedor read). In some examples, the difference between the resistivity ofdifferent logic states is referred to as the sensing window (or readwindow or memory window) of a memory cell, where a larger sensing windowmay be desirable.

In some cases, a sensing window of a memory cell is increased as thethreshold voltage window of a corresponding memory element is increased.As discussed herein, the bandgap of a phase change material may becorrelated with a threshold voltage window of a memory element, andthus, a sensing window of a memory cell may also be correlated with thebandgap of a phase change material—e.g., the sensing window of a memorycell may increase as the bandgap of a phase change material of acorresponding memory element increases, and vice versa. Accordingly,memory elements including phase change materials with wider bandgaps (ora “wide bandgap memory element”), such as IST or IGT, may result inlarger sensing windows for a memory cell than memory elements includingphase change materials with narrower bandgaps (or a “narrow bandgapmemory element”), such as GST. But, as also discussed herein, the SETspeed for wide bandgap memory elements is often slower than the SETspeed for narrow bandgap memory elements.

This relationship between sensing window and SET speed—i.e., as thesensing window increases, the SET speed become slower—may result in atrade-off between the reliability afforded by larger sensing windows andfaster throughput afforded by quicker SET speeds. In some cases, a SETspeed for a wide bandgap memory element may be insufficient to satisfytiming constraints of a memory operation. As such, in some cases, anarrow bandgap memory element may be used instead of the wide bandgapmemory element, despite the narrow bandgap memory element resulting in asmaller sensing window for the corresponding memory cell—e.g., to meettiming constraints.

The undesirable effects of the relationship between sensing window andSET speed may be emphasized as a size of a memory array is decreased. Asa phase change memory array is decreased in size, memory elements mayalso be decreased in size—e.g., decreased in height, width, and/ordepth—so that a similar or greater memory capacity may be achievedwithin a smaller footprint. And as discussed herein, as a size of amemory element containing a phase change material is reduced, athreshold voltage window of the memory element may also decrease. Toaccommodate for this size-based reduction in threshold voltage window,wide bandgap memory elements may be used in more compact memoryarrays—e.g., to maintain a similar sensing window and reliability for acorresponding memory cell. But as discussed herein, wide bandgap memoryelements containing are often correlated with slower SET speeds. And insome cases, the addition of a wide bandgap memory element may result innon-compliant memory operation—e.g., a failure to meet timingconstraints of a memory operation.

To increase throughput, memory density, and/or reliability of a memorycell, a memory element containing a phase change material having both alarge bandgap and a fast SET speed is desirable.

As discussed herein, a phase change material having both a large bandgapand a desirable SET speed may include a combination of Ge, Sb, Te, andat least one transition metal element selected from Group III of theperiodic table—such as yttrium (Y) or scandium (Sc)—which may also bereferred to as a Group III-Transition Metal (Group III-TM). In someexamples, the phase change material may be a Te-rich compositionincluding Ge in an amount ranging from 15 to 35 atomic percent (at. %);Sb in an amount less than or equal to 50 at. %; Te in an amount greaterthan or equal to 40 at. %; and at least one of Y or Sc in an amountranging from 0.15 at. % to 10 at. %. As discussed herein, a compositioncreated in accordance with the previous combination may have a largebandgap (e.g., between 0.6 and 0.9 electronvolts (eVs)) and a desirableSET speed (e.g., less than 10 μs). In some cases, the amount of Teincluded in the composition by atomic percent may be greater than 1) theamount of Ge included in the composition by atomic percent, 2) theamount of Sb included in the composition by atomic percent, or 3) theamount of Y and/or Sc included in the composition by atomic percent. Insome cases, as the amount of Y and/or Sc in the composition isincreased, a corresponding amount of Sb in the composition isdecreased—e.g., a proportional amount.

When a material as disclosed herein is incorporated into a memoryelement, the memory element may have a larger threshold voltage window.For example, a threshold voltage for a memory element having a givenheight and width may increase based on incorporating the material.Further, a memory element may benefit from this increase in thresholdvoltage window while maintaining SET speed (at least substantially orrelative to other chemistries with comparable threshold voltagewindows). For example, when a material of this composition isincorporated into a memory element, the memory element may have SETduration of less than 10 μs. Thus, by using such a material in a memoryelement, a reliability of a corresponding memory cell may beincreased—e.g., by enlarging a sensing window—without adverselyaffecting (or at least mitigating any adverse impact on) a throughput ofa memory array.

Also, when a material as disclosed herein is incorporated into a memoryelement the benefits of a larger threshold voltage window for the memoryelement may be maintained as a size of the memory element is decreased,while maintaining SET speed. For example, a threshold voltage for amemory element having a reduced height and/or width may increase basedon incorporating the material, with little to no reduction in SET speed.Thus, by using such a material in a memory element, a density of amemory array may be increased within a footprint—e.g., by reducing asize of the memory cells—without adversely affecting a reliability ofthe memory array—e.g., by having a same sensing window for the memorycells as for the memory cells used in a less dense memory array havingthe same footprint.

Features of the disclosure introduced above are further described belowin the context of a memory system. Specific examples are then describedof example compositions for transition metal doped GST and relatedmemory devices. These and other features of the disclosure are furtherillustrated by and described with reference to apparatus diagrams,system diagrams, and flowcharts that relate to transition metal dopedGST and related memory devices.

FIG. 1 illustrates an example of a memory array that supports transitionmetal doped GST in accordance with various aspects of the presentdisclosure. Memory array 100 may be configured to store electronicinformation and may include and may also be referred to as an electronicmemory apparatus. Memory array 100 includes memory cells 105 that areprogrammable to store different states.

Each memory cell 105 may be programmable to store two states, denoted alogic 0 and a logic 1. In some cases, memory cell 105 is configured tostore more than two logic states. A memory cell 105 may store chargerepresentative of the programmable states in a capacitor; for example, acharged and uncharged capacitor may represent two logic states,respectively. DRAM architectures may commonly use such a design, and thecapacitor employed may include a dielectric material with linear orpara-electric electric polarization properties as the insulator. Aferroelectric memory cell may similarly include a capacitor but with aferroelectric as the insulating material. Different levels ofpolarization of a ferroelectric capacitor may represent different logicstates. Ferroelectric materials have non-linear polarization propertiesand a ferroelectric material may store information when a voltage is notpresent across the ferroelectric material. Or in some cases,chalcogenide-based and/or phase change materials may be employed.Chalcogenides described herein may be in PCM storage elements orselector devices, or both.

Memory array 100 may be a three-dimensional (3D) memory array, wheretwo-dimensional (2D) memory arrays are formed on top of one another.This may increase the number of memory cells that may formed on a singledie or substrate as compared with 2D arrays, which in turn may reduceproduction costs or increase the performance of the memory array, orboth. According to the example depicted in FIG. 1, memory array 100includes two levels of memory cells 105 and may thus be considered athree-dimensional memory array; however, the number of levels is notlimited to two. Each level may be aligned or positioned so that memorycells 105 may be approximately aligned with one another across eachlevel, forming a memory cell stack 145. In accordance with the teachingsherein, memory array 100 may include a composition that includes Ge, Sb,Te, Sc, or Y, or some combination of these elements.

Each row of memory cells 105 is connected to an access line 110, andeach column of memory cells 105 is connected to a bit line 115. Accesslines 110 may also be known as word lines 110, and bit lines 115 mayalso be known digit lines 115. References to word lines and bit lines,or their analogues, are interchangeable without loss of understanding oroperation. Word lines 110 and bit lines 115 may be substantiallyperpendicular to one another to create an array. The two memory cells105 in a memory cell stack 145 may share a common conductive line suchas a digit line 115. That is, a digit line 115 may be in electroniccommunication with the bottom electrode of the upper memory cell 105 andthe top electrode of the lower memory cell 105. Other configurations maybe possible, for example, a third layer may share a word line 110 with alower layer. Or, the first and second layers may both have their ownword and bit line. That is, the top electrode of lower memory cell 105may be in electronic communication with a first digit line and thebottom electrode of upper memory cell 105 may be in electroniccommunication with a second digit line. In some cases, a third accessline may be present and may be used to activate and deactivate aselector device.

In general, one memory cell 105 may be located at the intersection oftwo conductive lines such as a word line 110 and a bit line 115. Thisintersection may be referred to as a memory cell's address. A targetmemory cell 105 may be a memory cell 105 located at the intersection ofan energized word line 110 and bit line 115; that is, a word line 110and bit line 115 may be energized in order to read or write a memorycell 105 at their intersection. Other memory cells 105 that are inelectronic communication with (e.g., connected to) the same word line110 or bit line 115 may be referred to as untargeted memory cells 105.

As discussed herein, electrodes may be coupled to a memory cell 105 anda word line 110 or a bit line 115. The term electrode may refer to anelectrical conductor, and in some cases, may be employed as anelectrical contact to a memory cell 105. An electrode may include atrace, wire, conductive line, conductive layer, or the like thatprovides a conductive path between elements or components of memoryarray 100.

Operations such as reading and writing may be performed on memory cells105 by activating or selecting a word line 110 and bit line 115, whichmay include applying a voltage or a current to the respective line. Wordlines 110 and bit lines 115 may be made of conductive materials, such asmetals (e.g., copper (Cu), aluminum (Al), gold (Au), tungsten (W),titanium (Ti), etc.), metal alloys, carbon, conductively dopedsemiconductors, or other conductive materials, alloys, or compounds.

Memory cells 105 may each have a memory element and a selector device. Aresistivity of a memory element may be programmed to correspond to aparticular logic state. In some cases, a memory element may include aphase change material. For example, a memory element may be or include achalcogenide material including a particular combination of the elementsGe, Sb, and Te, which may be referred to as a GST composition. In somecases, a GST composition may be doped with other elements, such asIn—e.g., to increase a bandgap of the GST composition. However, doping aGST composition with elements such as In may cause a SET speed of thecomposition to decrease (i.e., may cause the transition of thecomposition from an amorphous to a crystalline phase to take longer).

To increase a bandgap of a GST compound with little to no decrease, andin some cases an increase, in SET speed, GST may be doped with at leastone Group III-TM element—e.g., such as Y and/or Sc. In some cases,doping a GST composition by incorporating a Group III-TM element intothe GST composition may be accompanied by a corresponding decrease in anamount of Sb in the GST composition. In some cases, a transition metaldoped GST may have a bandgap between 0.6 eV and 0.9 eV and a SETduration that is less than 10 μs.

A selector device may be used to temporarily isolate a memory cell 105from the rest of memory array 100. For example, a memory cell 105 may beaccessed when a selector device is biased. In some cases, a selectordevice may include a metal-oxide-semiconductor field-effect transistor(MOSFET), bipolar junction transistor (BJT), diode, or ovonic thresholdswitch (OTS). In some cases, a selector device may include a phasechange material, such as a chalcogenide material. The selection ofmemory cell 105 may be a function of the threshold voltage of theselector device.

Accessing memory cells 105 may be controlled through a row decoder 120and a column decoder 130. For example, a row decoder 120 may receive arow address from the memory controller 140 and activate the appropriateword line 110 based on the received row address. Similarly, a columndecoder 130 receives a column address from the memory controller 140 andactivates the appropriate bit line 115. Thus, by activating a word line110 and a bit line 115, a memory cell 105 may be accessed.

Upon accessing, a memory cell 105 may be read, or sensed, by sensecomponent 125. For example, sense component 125 may be configured todetermine the stored logic state of memory cell 105 based on a signalgenerated by accessing memory cell 105. The signal may include a voltageor electrical current, and sense component 125 may include voltage senseamplifiers, current sense amplifiers, or both. For example, a currentmay be applied to a memory cell 105 and the magnitude of the voltage tocreate the current may depend on the electrical resistance or thresholdvoltage of the memory cell 105. Likewise, a voltage may be applied to amemory cell 105 (using the corresponding word line 110 and bit line 115)and the magnitude of the resulting current may depend on the electricalresistance and/or threshold voltage of the memory cell 105. In somecases, two or more different currents may develop based on a logic stateof memory cell 105. The difference between the two or more differentcurrents may be referred to as the memory (or sensing) window.

In some cases, a memory cell with a larger sensing window is morereliable than (e.g., may have less read errors) a memory cell having asmaller sensing window. In some cases, the sensing window corresponds toa threshold voltage window of a memory element in a memory cell 105. Insome cases, a sensing window of a memory cell 105 may be increased byincreasing a threshold voltage window of the memory element included inthe memory cell, where a threshold voltage window of the memory elementmay be increased by including a high bandgap phase change material inthe memory element. In some cases, a sensing window of a memory cell 105may be increased by using a memory element including a transition metaldoped GST compound, such as Y-GST or Sc-GST.

Sense component 125 may include various transistors or amplifiers inorder to detect and amplify a signal, which may be referred to aslatching. The latched signal may correspond to a logic state of memorycell 105 and may be output as output 135. In some cases, the accuracy ofsense component 125 is dependent on a sensing window for a memory cell.For example, a larger sensing window may allow for more variation in thevoltage or current induced on a digit line 115 by a memory cell 105 andprovided to the sense component 125 for sensing. In some cases, sensecomponent 125 may be a part of column decoder 130 or row decoder 120.Or, sense component 125 may be connected to or in electroniccommunication with column decoder 130 or row decoder 120.

A memory cell 105 may be set, or written, by similarly activating therelevant word line 110 and bit line 115—i.e., a logic value may bestored in the memory cell 105. Column decoder 130 or row decoder 120 mayaccept data, for example input/output 135, to be written to the memorycells 105. In the case of phase change memory, a memory cell 105 may bewritten by heating the memory element, for example, by passing a currentthrough the memory element until the memory element reaches a certaintemperature, which may be referred to as a glass transition temperature.After reaching the glass transition temperature, the memory element maybe quenched so as to, after cooling, be in a different phase than aninitial phase. The speed with which the memory element transitions froman amorphous phase to a crystalline phase may be referred to as thecrystallization speed or SET speed. In some cases, the SET speed limitsthe speed at which a logic state may be written to a memory cell 105. Insome examples, the duration for transitioning a memory element from anamorphous phase to a crystalline phase (which may be referred to as theSET duration) may exceed one or more timing constraints of a memoryoperation. In some cases, a SET speed of a memory cell 105 may beincreased or maintained without reducing or increasing a sensing windowof the memory cell 105 by using a memory element including a transitionmetal doped GST compound, such as Y-GST or Sc-GST, in the memory cell105.

In some cases, as a size of memory cells 105 is decreased (e.g., as asize of memory array 100 is decreased), and/or as the size of a memoryelement 220 is decreased (e.g., to have a height between 20 and 30 nmand width between 5 and 20 nm), a threshold voltage window of a memoryelement contained by the memory cell 105, along with a sensing window ofthe memory cell 105, may also decrease. In some cases, a memory elementincludes a phase change material having a wide bandgap (or a “widebandgap memory element”) may be used by a reduced-size memory cell 105to counteract the reduction in threshold voltage window. However, thewide bandgap memory element may be associated with a slower SET durationand the reduced-size memory cell 105 may lose compliance with one ormore memory system requirements—e.g., may fail to meet one or moretiming constraints.

As discussed herein, a wide bandgap memory element may include achalcogenide material including a particular combination of Ge, Sb, Te,and at least one Group III-TM element, such as Y and/or Sc. For example,the wide bandgap memory element may include Ge in an amount ranging from15 to 35 at. %; Sb in an amount less than or equal to 40 at. %; Te in anamount greater than or equal to 40 at. %; and at least one of Y or Sc inan amount ranging from 0.15 at. % to 10 at. % This memory element mayhave a wide bandgap (e.g., between 0.6 eV and 0.9 eV) and a short SETduration (e.g., <10 μs) and may be incorporated into a reduced-sizememory cell 105, which may benefit from the similar or larger sensingwindow of the wide bandgap memory element while maintaining SETcompliance.

In some memory architectures, accessing the memory cell 105 may degradeor destroy the stored logic state and re-write or refresh operations maybe performed to return the original logic state to memory cell 105. Butin non-volatile memory, such as chalcogenide-based or PCM, accessing thememory cell 105 may not destroy the logic state and, thus, the memorycell 105 may not require re-writing after accessing.

The memory controller 140 may control the operation (read, write,re-write, refresh, discharge, etc.) of memory cells 105 through thevarious components, for example, row decoder 120, column decoder 130,and sense component 125. In some cases, one or more of the row decoder120, column decoder 130, and sense component 125 may be co-located withthe memory controller 140. Memory controller 140 may generate row andcolumn address signals in order to activate the desired word line 110and bit line 115. Memory controller 140 may also generate and controlvarious voltage potentials or currents used during the operation ofmemory array 100. For example, it may apply discharge voltages to a wordline 110 or bit line 115 after accessing one or more memory cells 105.

In general, the amplitude, shape, or duration of an applied voltage orcurrent discussed herein may be adjusted or varied and may be differentfor the various operations discussed in operating memory array 100.Furthermore, one, multiple, or all memory cells 105 within memory array100 may be accessed simultaneously; for example, multiple or all cellsof memory array 100 may be accessed simultaneously during an operationin which all memory cells 105, or a group of memory cells 105, are setto a single logic state. The reliability with which the memorycontroller 140 may access memory cells 105 may increase for memory cells105 using a transition metal doped GST composition because the sensingwindow of memory cell 105 may be increased. At the same time, a timingwith which the memory controller 140 may access memory cells 105 mayremain the same or decrease for memory cells 105 using a transitionmetal doped GST composition because the SET speed of the memory cell 105may be maintained or reduced.

FIG. 2 illustrates an example cross-section of a memory array thatsupports transition metal doped GST in accordance with various aspectsof the present disclosure. Memory array 200 may be configured to storeelectronic data and may be an example of aspects of memory array 100 ofFIG. 1. Memory array 200 includes memory cell 105-a, first access line110-a (e.g. word line 110-a), and second access line 115-a (e.g. bitline 115-a), which may be examples of a memory cell 105, word line 110,and bit line 115, as described with reference to FIG. 1.

In some cases, a three-dimensional (3D) memory array may be formed bystacking multiple memory arrays 200 on one another. The two stackedarrays may, in some examples, have common conductive lines such thateach level may share word lines 110 or bit lines 115 as described withreference to FIG. 1. In some examples, memory array 200 may includeadditional access lines, including an additional access line that is inelectronic communication with selector device 215. For example, whenselector device 215 is a three-terminal device, an additional accessline may be used to activate and deactivate selector device 215.

Memory array 200 may be referred to as a cross-point architecture. Itmay also be referred to as a pillar structure. For example, as shown inFIG. 2, a pillar may be in contact with a first conductive line (firstaccess line 110-a) and a second conductive line (bit line 115-a), wherethe pillar comprises first electrode 210, selector device 215, andmemory cell 105-a, which may include second electrode 225, memoryelement 220, and third electrode 205. First electrode 210 may bereferred to as bottom electrode 210, second electrode 225 may bereferred to as middle electrode 225 or as the bottom electrode of memorycell 105-a, and third electrode 205 may be referred to as top electrode205.

Such a pillar architecture may offer relatively high-density datastorage with lower production costs compared to other memoryarchitectures. For example, the cross-point architecture may have memorycells with a reduced area and, resultantly, an increased memory celldensity compared to other architectures. For example, the architecturemay have a 4F² memory cell area, where F is the smallest feature size,compared to other architectures with a 6F² memory cell area, such asthose with a three-terminal selection.

Memory cell 105-a may be electronically programmable to be in differentstates and may be configured to store a logic value corresponding to aparticular state. Memory cell 105-a includes second electrode 225, thirdelectrode 205, and memory element 220, which may include a phase changematerial. Memory cell 105-a may be a target memory cell.

Selector device 215 may, in some cases, be connected in series between amemory cell 105 and a conductive line, for example, between memory cell105-a and at least one of first access line 110-a or bit line 115-a. Forexample, as depicted in FIG. 2, selector device 215 may be locatedbetween bottom electrode 210 and middle electrode 225; thus, selectordevice 215 is located in series between memory cell 105-a and firstaccess line 110-a. Other configurations are possible. For example,selector device 215 may be located in series between memory cell 105-aand bit line 115-a. Selector device 215 may aid in selecting aparticular memory cell 105-a or may help prevent stray currents fromflowing through non-selected memory cells 105-a adjacent a selectedmemory cell 105-a. For example, selector device 215 may have a thresholdvoltage such that a current flows through selector device 215 when thethreshold voltage is met or exceeded. The selection of memory cell 105-amay be a function of the threshold voltage of the selector device 215.Selector device 215 may also be referred to as a selection component. Insome cases, selector device 215 may include a metal-oxide-semiconductorfield-effect transistor (MOSFET), bipolar junction transistor (BJT),diode, or ovonic threshold switch (OTS).

Selector device 215 may be coupled with the memory element 220. Theselector device 215 and the memory element 220 may be arranged in aseries configuration between the first access line 110-a and the bitline 115-a. A selector device 215 may include a first chalcogenidematerial. In some cases, a selector device 215 may comprise a firstchalcogenide material and a memory element 220 may comprise a differentcomposition (e.g., a second chalcogenide material) than the selectordevice 215. Although the example of memory array 200 illustrated in FIG.2 includes a separate memory element and selector device, in some cases,a memory cell 105 may not include a separate memory element and selectordevice. This type of memory architecture may be referred to asself-selecting memory, and the selector device 215 may serve as thememory element, or vice versa. A memory device may therefore include amemory cell that comprises a self-selecting memory device. For example,a single element that includes a chalcogenide material may serve as botha memory element and a selector device such that a separate selectordevice may be unncessary.

Memory element 220 may include a material having a programmableresistance. In some cases, the material may exhibit a differentresistivity (e.g., resistance and/or voltage threshold) based on a phase(e.g., amorphous phase or crystalline phase) of the material, and may bereferred to a phase change material. As discussed herein, a phase of thephase change material may be changed by applying and removing voltagesto/from memory element 220.

Memory element 220 may be accessed via selector device 215. For example,when a voltage across selector device 215 reaches a threshold value,current may flow between access lines 110-a and 115-a through memoryelement 220. This flow of current may be used to write a logic value tomemory element 220. A write operation may include applying a voltage tomemory element 220 that heats memory element 220 to a glass transitiontemperature. After memory element 220 reaches the glass transitiontemperature, the voltage may be removed and the memory element 220 maycool. During the cooling period, the atoms within memory element 220 maybe arranged in accordance with a particular phase. For example, for acrystalline phase, octahedral bonding geometry may form between all ormost atoms of memory element 220, and for an amorphous phase, varyingbonding configurations may form between the atoms of memory element 220.Whether memory element 220 exhibits a crystalline phase or an amorphousphase may be based on how the voltage is removed from and whetheradditional voltage is applied to memory element 220 during the coolingperiod.

To store a different logic value at memory element 220 that is in anamorphous phase, the write operation may include transitioning memoryelement 220 from the amorphous phase to a crystalline phase. Theduration for transitioning memory element 220 from an amorphous to acrystalline phase may be referred to as the SET duration. In some cases,a length of the SET duration for memory element 220 is based on acomposition that includes memory element 220. For instance, the SETduration may be shorter for certain compositions than for others. Asdiscussed herein, the SET duration may be correlated with the thresholdvoltage window of memory element 220—e.g., as the threshold voltagewindow increases, a length the SET duration also increases.

A flow of current through memory element 220 may also be used to read alogic value stored at memory element 220. When reading memory element220, the difference between the threshold voltage across selector device215 at which current begins to flow and the threshold voltage window ofmemory element 220 may be referred to as a sensing window. In somecases, the larger the sensing window of memory element 220, the morereliable memory cell 105-a. As discussed herein, the threshold voltagewindow of memory element may be based on a size of memory element220—e.g., as memory element 220 is decreased in size, the thresholdvoltage window may also decrease—and/or a bandgap of a compositionincluded in memory element 220—e.g., as a bandgap of the compositionincreases, the threshold voltage window of memory element 220 increases.However, as discussed herein, increasing the threshold voltage window ofmemory element 220 may result in a decrease in a SET duration for memoryelement 220. Similarly, when a size of memory element 220 is decreased,using compositions with higher bandgaps to increase a threshold voltagewindow of memory element 220 may also result in a decrease in a SETduration for memory element 220.

As discussed herein, in some cases, memory element 220 includes a highbandgap composition that increases a threshold voltage window of memoryelement 220 while maintaining or increasing a SET speed of memoryelement 220. For example, memory element include a phase change materialthat includes a combination of Ge, Sb, Te, and at least one Group III-TMelement. For example, memory element 220 may include a phase changematerial that includes Ge in an amount ranging from 15 to 35 at. % ofthe composition; Sb in an amount less than or equal to 50 at. % of thecomposition; Te in an amount greater than or equal to 40 at. % of thecomposition, and at least one element selected from a group consistingof yttrium and scandium, in an amount ranging from 0.15 to 10 at. % ofthe composition. As discussed herein, a composition created inaccordance with these ranges may have a large bandgap (e.g., between 0.6and 0.9 electronvolts (eVs)) and a quick SET speed (e.g., less than 10μs).

Memory array 200 may be made by various combinations of materialformation and removal. For example, layers of material may be depositedthat correspond to the first access line 110-a, bottom electrode 210,selector device 215, middle electrode 225, memory element 220, and topelectrode 205. Material may be selectively removed to then create thedesired features, such as the pillar structure depicted in FIG. 2. Forexample, features may be defined using photolithography to pattern aphotoresist and then material may be removed by techniques such asetching. Bit line 115-a may then be formed, for example, by depositing alayer of material and selectively etching to form the line structuredepicted in FIG. 2. In some cases, electrically insulating regions orlayers may be formed or deposited. The electrically insulating regionsmay include oxide or nitride materials, such as silicon oxide, siliconnitride, or other electrically insulating materials

Various techniques may be used to form materials or components of memoryarray 200. These may include, for example, chemical vapor deposition(CVD), metal-organic chemical vapor deposition (MOCVD), physical vapordeposition (PVD), sputter deposition, atomic layer deposition (ALD), ormolecular beam epitaxy (MBE), among other thin film growth techniques.Material may be removed using a number of techniques, which may include,for example, chemical etching (also referred to as “wet etching”),plasma etching (also referred to as “dry etching”), orchemical-mechanical planarization.

FIG. 3 illustrates an example of a plot that illustrates characteristicsof transition metal doped GST in accordance with various aspects of thepresent disclosure. Plot 300 illustrates a relationship between arelative crystallization speed of a memory element and a sensing windowfor a memory element and/or memory cell, such as memory element 220(and/or selector device 215) and memory cell 105-a of FIG. 2, in termsof voltage. Plot 300 includes sensing window axis 305, SET speed axis310, trend line 315, and region 320 for a transition metal-doped GST.

Sensing window axis 305 provides sensing window values in an increasingorder from left to right. That is, the left side of sensing window axis305 corresponds to small sensing windows while the right side of sensingwindow axis 305 corresponds to larger, more desirable sensing windows.As discussed herein, a sensing window for a memory cell may be relatedto a threshold voltage window of a corresponding memory element—e.g., amemory element having a high threshold voltage window often correspondsto a memory cell having a large sensing window. And the thresholdvoltage window of a memory element may be related to a size of thememory element—e.g., a threshold voltage window of a memory elementoften decreases as the size of a memory element is decreased—and abandgap of a composition included in the memory element—e.g., acomposition with a larger bandgap often results in a memory elementhaving a larger threshold voltage window.

SET speed axis 310 provides SET speed values in a decreasing order fromtop to bottom. That is, the bottom of SET speed axis 310 corresponds toslower crystallization speeds while the top of SET speed axis 310corresponds to faster, more desirable crystallization speeds. Asdiscussed herein, a SET speed for a memory cell may be related to abandgap of a corresponding memory element—e.g., a memory element havinga large bandgap often has a slow SET speed.

In some cases, a bandgap of a GST composition may be based on the Sb—Tebonds of the GST composition. In some cases, the bandgap of the GSTcomposition may be increased by replacing Sb atoms (which has anelectronegativity of 2.05) with atoms having a higher electronegativitydifference relative to Te (which has an electronegativity of 2.10), suchas In atoms (In has an electronegativity of 1.78). However, increasingthe bandgap of the doped composition by replacing the Sb atoms withelements having a higher electronegativity difference relative to Te,such as In, may also decrease a SET speed of the doped composition—e.g.due to the tetrahedral bonds of In which decrease the number offour-fold rings, which may act as nuclei for crystallization. Thus, forexample, a composition with more four-fold rings may have a faster SETspeed than a composition with less four-fold rings.

Thus, as a threshold voltage window of a memory element, and a sensingwindow of a corresponding memory cell, is increased—e.g., by selecting acomposition having a large bandgap for the memory element—a SET speed ofthe memory element, and the corresponding memory cell, often decreases.Trend line 315 illustrates this relationship between sensing window sizeand crystallization speed for a memory element/cell.

This relationship suggests a trade-off between compositions with highbandgaps and compositions with high SET speeds when selecting acomposition to use for a memory element. That is, compositions withnarrow bandgaps and higher SET speeds may in some cases be used for thememory element despite a smaller sensing window resulting for acorresponding memory cell. For example, material compositions used inmemory cells represented by trend line 315 may be pure GST compositions(i.e. including only Ge, Sb, Te) or Q-GST compositions where Q may be anelement that is not a Group III-TM element (e.g., In-GST). Somecompositions used for memory elements/cells represented by trend line315 may include IST, GST, IGT, and the like.

The effects of the sensing window/SET speed relationship may be furtheremphasized as a size of memory cells are decreased. As discussed herein,a threshold voltage window of a memory element, and thus a sensingwindow of a memory cell, may decrease as a size of the memory element isdecreased. Thus, a memory element using a first composition may have afirst threshold voltage window at a first size and a second thresholdvoltage window at a second size, while a SET speed of the memory elementmay be relatively unchanged. And as a size of memory elements continuesto decrease—e.g., to increase the density of a memory array—compositionswith larger bandgaps may be used to increase a sensing window of acorresponding memory cell. But as discussed herein, using compositionswith larger bandgaps may cause a SET speed of the memory cell to slow.In some cases, the SET speed of a memory cell can slow to a degree thata duration for transitioning a corresponding memory element from anamorphous to crystalline phase (which may be referred to as the SETduration) exceeds a timing constraint for a memory operation.

To increase a reliability and/or throughput of a memory system, a memorysystem may employ a composition as disclosed herein, which results in adeviation of a memory cell from trend line 315—i.e., a compositionhaving a relatively high bandgap and a relatively fast SET speed thatresults in a memory cell with a relatively large sensing window and arelatively fast SET speed.

For example, as disclosed herein a memory cell containing a memoryelement using a composition that includes a combination of Ge, Sb, Te,and a Group III-TM element may have a relatively high sensing window anda relatively fast SET speed, represented by region 320—region 320 mayencompass a range of sensing window/SET speed combinations achievable bya composition using a combination of Ge, Sb, Te, and a Group III-TMelement. As discussed herein, a bandgap of GST may be based on its Sb—Tebonds and increased by replacing Sb atoms with atoms of an elementhaving higher electronegativity difference relative to Te. Group III-TMelements, such as Y (which has an electronegativity of 1.22) or Sc(which has an electronegativity of 1.36), may also have a higherelectronegativity difference relative to Te than Sb, and may be used toincrease a bandgap of the GST composition. However, Group III-TMelements, such as Y and Sc, may be introduced to a GST composition withlittle to no decrease, or an increase, in the SET speed of the GSTcomposition. The SET speed of the Group III-TM doped GST may bemaintained or increased due to the d-type orbitals of the Group III-TMelements, which do not depress the formation of four-fold rings, whichact as nuclei for crystallization. Such a composition is discussed inmore detail herein, and at least with reference to FIG. 4.

It is worth noting that doping an Sb—Te (ST) composition, such asSb₂Te₃, with a Group III-TM element (e.g., to create Sc—Sb—Te (ScST) orY—Sb—Te (YST)) may fail to provide a composition with a wide bandgap anda desirable SET speed. In some cases, doping an ST composition with aGroup III-TM element may fail to provide a wide bandgap compositionbecause of the relatively narrower bandgap of the baseline STcomposition (e.g., around 0.55 eV). That is, the effect of the GroupIII-TM doping on an ST composition may not be strong enough to yield aGroup III-TM doped ST composition with a wide bandgap (e.g., greaterthan 0.65 eV).

By way of example, a composition included in a memory elementcorresponding to a sensing window/SET speed combination within region320 may have Ge in an amount ranging from 15 to 35 at. %, Sb in anamount less than or equal to 50 at. %, Te in an amount greater than orequal to 40 at. %, and at least one element selected from a groupconsisting of Y and Sc, in an amount ranging from 0.15 to 10 at. %. Thiscomposition may have a bandgap energy value ranging from 0.6 to 0.9 eVsand a SET speed that corresponds to a SET duration of less than 10 μs.In some cases, such a composition may be used in memory cells toincrease a reliability of a corresponding memory array—e.g., byincreasing a sensing window of the memory cells while maintaining orreducing SET duration. Such a composition may also be used in memorycells to maintain a sensing window of the memory cells as a size of acorresponding memory array is decreased.

FIG. 4 illustrates an example ternary diagram showing example transitionmetal doped GST compositions in accordance with various aspects of thepresent disclosure. Plot 400 illustrates first axis 405, second axis 410and third axis 415.

First axis 405 may represent atomic percentages of Ge. Second axis 410may represent atomic percentages of Sb. Third axis 415 may representatomic percentages of Te. Region 420 may encompass different GSTcompositions that may be doped with a Group III-TM element, such as Y orSc. Data point 425 may represent a composition that includes GST priorto the addition of a Group III-TM element.

As described herein, compositions with an increased or maintained energybandgap and a maintained or increased SET speed/reduced SET duration maybe useful for memory elements and may include some combination of Ge,Sb, Te, and at least one Group III-TM element. A chalcogenide materialcomposition may result in the general formula Ge_(x)Sb_(y)Te_(z)Q_(w),where Q is one of the Group III-TM elements. A Group III-TM element maybe at least one element selected from a group consisting of Y or Sc. Asdiscussed herein, a chalcogenide material composition may be comprisedof the compositions identified in Table 1, which may provide compositionranges by atomic percentages of Ge, Sb, Te, and a Group III-TM element.

TABLE 1 Ge Sb Te Group III-TM elements First (at. %) 15-35 ≤50 ≥400.15-10 Second (at. %) 15-35 25-35 ≥40 0.15-10 Third (at. %) 25-45 0 ≥400.15-20

As shown in Table 1, the GST composition may be doped so that thetransition metal-doped GST composition includes a Group III-TM elementin an amount ranging from 0.15 to 10 at. %. In some cases, a bandgap ofthe composition ranges from 0.6 to 0.9 electronvolts and may have acrystallization speed that is less than 10 μs.

In some cases, an increase in the atomic percent of the Group III-TMelement in the Group III-TM doped GST results in a correspondingdecrease in the Sb of the GST composition. In some examples, the Sb ofthe GST composition may be completely replaced by the transition metalin the transition metal doped GST composition resulting in a GroupIII-TM doped GT composition (e.g., ScGT or YGT). When the Sb of the GSTis completely replaced by a Group III-TM element, such as Sc or Y, theamount of Ge or Te in the Group III-TM doped GT composition may beincreased accordingly—for example, the composition may include a GroupIII-TM element in an amount ranging from 0.15 to 20 at. % and the at. %of the Ge and Te may collectively compose 80 at. % or more of the GroupIII-TM doped GT composition.

In some examples, the amount of the Group III-TM element is less than 5at. % of the transition metal doped GST composition. In some cases, theamount of germanium ranges from 15 to 25 at. % of the composition. Insome cases, the amount of antimony ranges from 10 to 40 at. % of thecomposition. In some cases, the amount of tellurium by atomic percent isgreater than the amount of germanium by atomic percent, is greater thanthe amount of antimony by atomic percent, and is greater than the amountof the at least one element by atomic percent (which may be referred toas a Te-rich composition). In some cases, the amount of tellurium rangesfrom 40 to 65 at. % of the composition. In some cases, the amount oftellurium ranges from 45 at. % to 55 at. % of the composition.

In some examples, a GST composition is doped to include 4 at. % of aGroup III-TM element. For example, data point 425 may correspond to aGST composition including Ge in an amount of approximately 22 at. %, Sbin amount of approximately 32 at. %, and Te in an amount ofapproximately 46 at. % that is doped with Y in an amount of 4 at. %,which may result in a Y-GST composition including Ge in an amount ofapproximately 22 at. %, Sb in amount of approximately 28 at. %, Te in anamount of approximately 46 at. %, and Y in amount of 4 at. %. Such aY-GST composition may have a bandgap of 0.67 eV and a SET speed of lessthan 10 μs.

FIG. 5 illustrates an example memory array that supports transitionmetal doped GST in accordance with various embodiments of the presentdisclosure. Memory array 500 may be referred to as an electronic memoryapparatus and includes memory controller 140-a and memory cell 105-b,which may be examples of memory controller 140 and memory cell 105described with reference to FIG. 1. Memory array 500 may also includereference component 520 and latch 525. The components of memory array500 may be in electronic communication with each other and may performthe functions described with reference to FIG. 1. In some cases,reference component 520, sense component 125-a and latch 525 may becomponents of memory controller 140-a.

Reference component 520 may include various components to generate areference signal for sense component 125-a. Reference component 520 mayinclude circuitry configured to produce a reference signal.

Memory cell 105-b may include one or more memory elements. Each of thememory elements may include a composition that includes a particularcombination of Ge, Sb, Te, and one or more Group III-TM elements. Abandgap of the composition may be between 0.6 to 0.9 eV and a SET speedof the composition may be less than 10 μs.

Sense component 125-a may compare a signal from memory cell 105-b(through bit line 115-b) with a reference signal from referencecomponent 520. Upon determining the logic state, the sense component maythen store the output in latch 525, where it may be used in accordancewith the operations of an electronic device that memory array 500 is apart.

Memory controller 140-a may, in combination with other components applyvoltages throughout memory array 500, write data to memory cells 105-b,read data from memory cells 105-b, and generally operate memory array500 as described in FIG. 1. Memory controller 140-a may include biasingcomponent 510 and timing component 515. Memory controller 140-a may bein electronic communication with word line 110-b, bit line 115-b, sensecomponent and 125-a, which may be examples of a word line 110, bit line115, and sense component 125, as described with reference to FIG. 1.

Memory controller 140-a may be configured to activate word line 110-b orbit line 115-b by applying voltages to those various nodes. For example,biasing component 510 may be configured to apply a voltage to operatememory cell 105-b to read or write memory cell 105-b as describedherein. In some cases, memory controller 140-a may include a rowdecoder, column decoder, or both, as described with reference to FIG. 1.This may enable memory controller 140-a to access one or more memorycells 105. Biasing component 510 may also provide voltage potentials toreference component 520 in order to generate a reference signal forsense component 125-a. Additionally, biasing component 510 may providevoltage potentials for the operation of sense component 125-a.

In some cases, memory controller 140-a may perform its operations usingtiming component 515. For example, timing component 515 may control thetiming of the various word line selections or plate biasing, includingtiming for switching and voltage application to perform the memoryfunctions, such as reading and writing, discussed herein. In some cases,timing component 515 may control the operations of biasing component510.

In some cases, memory controller 140-a may be used to access memorycell(s) 105-b for memory operations (such as read and write operations).For example, memory controller 140-a may select, for a memory operation,memory cell(s) 105-b comprising a memory element having a compositioncomprising: germanium in an amount ranging from 15 atomic percent (at.%) to 35 at. %; antimony in an amount less than or equal to 50 at. %;tellurium in an amount greater than or equal to 40 at. %; and at leastone element selected from a group consisting of yttrium and scandium, inan amount ranging from 0.15 at. % to 10 at. %; and apply, during thememory operation, one or more voltages to the memory cell(s) 105-b basedat least in part on the memory operation and the composition

FIG. 6 illustrates an example system that supports transition metaldoped GST in accordance with various embodiments of the presentdisclosure. System 600 includes a device 605, which may be or include aprinted circuit board to connect or physically support variouscomponents. Device 605 includes a memory array 100-a, which may be anexample of memory array 100 described with reference to FIG. 1. Memoryarray 100-a may contain memory controller 140-b and memory cell(s)105-c, which may be examples of memory controller 140 and memory cells105 described with reference to FIGS. 1 and 5. Device 605 may alsoinclude a processor 610, BIOS component 615, peripheral component(s)620, and input/output control component 625. The components of device605 may be in electronic communication with one another through bus 630.

Processor 610 may be configured to operate memory array 100-a throughmemory controller 140-b. In some cases, processor 610 may perform thefunctions of memory controller 140 described with reference to FIGS. 1and 5. In other cases, memory controller 140-b may be integrated intoprocessor 610. Processor 610 may be a general-purpose processor, adigital signal processor (DSP), an application-specific integratedcircuit (ASIC), a field-programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or it may be a combination of these types ofcomponents, and processor 610 may perform various functions describedherein. Processor 610 may, for example, be configured to executecomputer-readable instructions stored in memory array 100-a to causedevice 605 perform various functions or tasks.

BIOS component 615 may be a software component that includes a basicinput/output system (BIOS) operated as firmware, which may initializeand run various hardware components of system 600. BIOS component 615may also manage data flow between processor 610 and the variouscomponents, e.g., peripheral components 620, input/output controlcomponent 625, etc. BIOS component 615 may include a program or softwarestored in read-only memory (ROM), flash memory, or any othernon-volatile memory.

Peripheral component(s) 620 may be any input or output device, or aninterface for such devices, that is integrated into device 605. Examplesmay include disk controllers, sound controller, graphics controller,Ethernet controller, modem, universal serial bus (USB) controller, aserial or parallel port, or peripheral card slots, such as peripheralcomponent interconnect (PCI) or accelerated graphics port (AGP) slots.

Input/output control component 625 may manage data communication betweenprocessor 610 and peripheral component(s) 620, input devices 635, oroutput devices 640. Input/output control component 625 may also manageperipherals not integrated into device 605. In some cases, input/outputcontrol component 625 may represent a physical connection or port to theexternal peripheral.

Input 635 may represent a device or signal external to device 605 thatprovides input to device 605 or its components. This may include a userinterface or interface with or between other devices. In some cases,input 635 may be a peripheral that interfaces with device 605 viaperipheral component(s) 620 or may be managed by input/output controlcomponent 625.

Output 640 may represent a device or signal external to device 605configured to receive output from device 605 or any of its components.Examples of output 640 may include a display, audio speakers, a printingdevice, another processor or printed circuit board, etc. In some cases,output 640 may be a peripheral that interfaces with device 605 viaperipheral component(s) 620 or may be managed by input/output controlcomponent 625.

The components of memory controller 140-b, device 605, and memory array100-a may be made up of circuitry designed to carry out their functions.This may include various circuit elements, for example, conductivelines, transistors, capacitors, inductors, resistors, amplifiers, orother active or inactive elements, configured to carry out the functionsdescribed herein.

FIG. 7 illustrates a flowchart of a method or methods for transitionmetal doped GST in accordance with various embodiments of the presentdisclosure. Method 700 may illustrate aspects of programming aresistance of a memory cell containing a Group III-TM doped GSTcomposition.

At block 705, the method may include selecting, for a memory operation,a memory cell comprising a memory element having a compositioncomprising: Ge in an amount ranging from 15 atomic percent (at. %) to 35at. %; Sb in an amount less than or equal to 50 at. %; Te in an amountgreater than or equal to 40 at. %; and at least one element selectedfrom a group consisting of Y and Sc, in an amount ranging from 0.15 at.% to 10 at. %, as described with reference to FIGS. 1-5. In certainexamples, the operations of block 705 may be performed or facilitated bya memory controller, as described with reference to FIGS. 1, 5, and 6.

At block 710, the method may include applying, during the memoryoperation, one or more voltages to the memory cell based at least inpart on the memory operation and the composition, as described withreference to FIGS. 1-5. In certain examples, the operations of block 710may be performed or facilitated by a memory controller, as describedwith reference to FIGS. 1, 5, and 6.

In some examples, an apparatus as described herein may perform a methodor methods, such as the method 700. The apparatus may include features,means, or instructions (e.g., a non-transitory computer-readable mediumstoring instructions executable by a processor) for selecting, for amemory operation, a memory cell comprising a memory element having acomposition comprising: Ge in an amount ranging from 15 atomic percent(at. %) to 35 at. %; Sb in an amount less than or equal to 50 at. %; Tein an amount greater than or equal to 40 at. %; and at least one elementselected from a group consisting of Y and Sc, in an amount ranging from0.15 at. % to 10 at. %; and applying, during the memory operation, oneor more voltages to the memory cell based at least in part on the memoryoperation and the composition.

It should be noted that the methods described above describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Furthermore, embodiments from two or more of the methods may becombined.

In some examples, an apparatus or device may perform aspects of thefunctions described herein using general, or special-purpose hardware.For example, an apparatus or device may include a selector device and amemory element coupled with the selector device, the memory elementhaving a composition comprising: Ge in an amount ranging from 15 at. %to 35 at. %; Sb in an amount less than or equal to 50 at. %; Te in anamount greater than or equal to 40 at. %; and at least one elementselected from a group consisting of Y and Sc in an amount ranging from0.15 at. % to 10 at. %.

In some examples of the apparatus or device, the at least one elementselected from the group is yttrium. In some examples of the apparatus ordevice, the amount of the yttrium ranges from 1 at. % to 5 at. %.

In some examples of the apparatus or device, a height of the memoryelement ranges from 20 nanometers to 40 nanometers and a width of thememory element ranges from 5 nanometers to 50 nanometers.

In some examples of the apparatus or device, a bandgap of the memoryelement ranges from 0.6 electronvolts and 0.9 electronvolts and acrystallization speed of the memory element is less than 10microseconds.

In some examples of the apparatus or device, the selector devicecomprises any one of a metal-oxide-semiconductor field-effect transistor(MOSFET), bipolar junction transistor (BJT), diode, or an ovonicthreshold switch.

In another example, an apparatus or device may include a first accessline; a second access line; a first memory cell that includes achalcogenide material comprising a composition that includes germanium,antimony, tellurium, and at least one of yttrium and scandium, whereinthe first access line is coupled with the second access line via thefirst memory cell.

In some examples of the apparatus or device, the composition thatincludes the chalcogenide material comprises: Ge in an amount rangingfrom 15 at. % to 35 at. %; Sb in an amount less than or equal to 50 at.%; Te in an amount greater than or equal to 40 at. %; and at least oneelement selected from a group consisting of Y and Sc in an amountranging from 0.15 at. % to 10 at. %.

In some examples of the apparatus or device, the at least one elementselected from the group is yttrium. In some examples of the apparatus ordevice, an amount of the yttrium ranges from 0.5 at. % to 5 at. %.

In some examples, the apparatus or device includes a second memory cellcoupled with the first memory cell, wherein a distance between a centerof the second memory cell and a center of the first memory cell rangesfrom 10 nanometers to 45 nanometers.

In some examples of the apparatus or device, the first access line andthe second access line are arranged in a three dimensional cross-pointconfiguration and the apparatus or device includes a third access line,wherein the first access line and the third access line are arranged inthe three dimensional cross-point configuration and are coupled with thesecond memory cell.

In some examples of the apparatus or device, the first memory cellcomprises a selector device and a memory element that comprises thechalcogenide material, wherein a height of the memory element rangesfrom 20 nanometers to 40 nanometers and a width of the memory elementranges from 5 nanometers to 50 nanometers.

In some examples, the apparatus or device includes a selector device anda third access line that is coupled with the selector device andelectronically isolated from the memory cell by the selector device.

The description herein provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate.Also, features described with respect to some examples may be combinedin other examples.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The terms “example,” “exemplary,” and “embodiment,” as usedherein, mean “serving as an example, instance, or illustration,” and not“preferred” or “advantageous over other examples.” The detaileddescription includes specific details for the purpose of providing anunderstanding of the described techniques. These techniques, however,may be practiced without these specific details. In some instances,well-known structures and devices are shown in block diagram form inorder to avoid obscuring the concepts of the described examples.

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. When the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

The term “electronic communication” and “coupled” refer to arelationship between components that support electron flow between thecomponents. This may include a direct connection between components ormay include intermediate components. Components in electroniccommunication or coupled to one another may be actively exchangingelectrons or signals (e.g., in an energized circuit) or may not beactively exchanging electrons or signals (e.g., in a de-energizedcircuit) but may be configured and operable to exchange electrons orsignals upon a circuit being energized. By way of example, twocomponents physically connected via a switch (e.g., a transistor) are inelectronic communication or may be coupled regardless of the state ofthe switch (i.e., open or closed).

The term “isolated” or “electrically isolated” refers to a relationshipbetween components in which electrons are not presently capable offlowing between them; components are isolated from each other if thereis an open circuit between them. For example, two components physicallyconnected by a switch may be isolated from each other when the switch isopen.

The term “layer” used herein refers to a stratum or sheet of ageometrical structure. Each layer may have three dimensions (e.g.,height, width, and depth) and may cover some or all of a surface. Forexample, a layer may be a three-dimensional structure where twodimensions are greater than a third. Layers may include differentelements, components, and/or materials. In some cases, one layer may becomposed of two or more sublayers. In some of the appended figures, twodimensions of a three-dimensional layer are depicted for purposes ofillustration. Those skilled in the art will, however, recognize that thelayers are three-dimensional in nature.

As used herein, the term “substantially” means that the modifiedcharacteristic (e.g., a verb or adjective modified by the termsubstantially) need not be absolute but is close enough so as to achievethe advantages of the characteristic.

As used herein, the term “electrode” may refer to an electricalconductor, and in some cases, may be employed as an electrical contactto a memory cell or other component of a memory array. An electrode mayinclude a trace, wire, conductive line, conductive layer, or the likethat provides a conductive path between elements or components of memoryarray 100.

The term “photolithography,” as used herein, may refer to the process ofpatterning using photoresist materials and exposing such materials usingelectromagnetic radiation. For example, a photoresist material may beformed on a base material by, for example, spin-coating the photoresiston the base material. A pattern may be created in the photoresist byexposing the photoresist to radiation. The pattern may be defined by,for example, a photo mask that spatially delineates where the radiationexposes the photoresist. Exposed photoresist areas may then be removed,for example, by chemical treatment, leaving behind the desired pattern.In some cases, the exposed regions may remain and the unexposed regionsmay be removed.

The devices discussed herein, including memory array 100, may be formedon a semiconductor substrate, such as silicon, germanium,silicon-germanium alloy, gallium arsenide, gallium nitride, etc. In somecases, the substrate is a semiconductor wafer. In other cases, thesubstrate may be a silicon-on-insulator (SOI) substrate, such assilicon-on-glass (SOG) or silicon-on-sapphire (SOP), or epitaxial layersof semiconductor materials on another substrate. The conductivity of thesubstrate, or sub-regions of the substrate, may be controlled throughdoping using various chemical species including, but not limited to,phosphorus, boron, or arsenic. Doping may be performed during theinitial formation or growth of the substrate, by ion-implantation, or byany other doping means.

Chalcogenide materials may be materials or alloys that include at leastone of the elements S, Se, and Te. Phase change materials discussedherein may be chalcogenide materials. Chalcogenide materials may includealloys of S, Se, Te, Ge, As, Al, Sb, Au, indium (In), gallium (Ga), tin(Sn), bismuth (Bi), palladium (Pd), cobalt (Co), oxygen (O), silver(Ag), nickel (Ni), platinum (Pt). Example chalcogenide materials andalloys may include, but are not limited to, Ge—Te, In—Se, Sb—Te, Ga—Sb,In—Sb, As—Te, Al—Te, Ge—Sb—Te, Te—Ge—As, In—Sb—Te, Te—Sn—Se, Ge—Se—Ga,Bi—Se—Sb, Ga—Se—Te, Sn—Sb—Te, In—Sb—Ge, Te—Ge—Sb—S, Te—Ge—Sn—O,Te—Ge—Sn—Au, Pd—Te—Ge—Sn, In—Se—Ti—Co, Ge—Sb—Te—Pd, Ge—Sb—Te—Co,Sb—Te—Bi—Se, Ag—In—Sb—Te, Ge—Sb—Se—Te, Ge—Sn—Sb—Te, Ge—Te—Sn—Ni,Ge—Te—Sn—Pd, or Ge—Te—Sn—Pt.

The hyphenated chemical composition notation, as used herein, indicatesthe elements included in a particular compound or alloy and is intendedto represent all stoichiometries involving the indicated elements. Forexample, Ge—Te may include Ge_(x)Te_(y), where x and y may be anypositive integer. Other examples of variable resistance materials mayinclude binary metal oxide materials or mixed valence oxide includingtwo or more metals, e.g., transition metals, alkaline earth metals,and/or rare earth metals. Embodiments are not limited to a particularvariable resistance material or materials associated with the memoryelements of the memory cells. For example, other examples of variableresistance materials can be used to form memory elements and may includechalcogenide materials, colossal magnetoresistive materials, orpolymer-based materials, among others.

A transistor or transistors discussed herein may represent afield-effect transistor (FET) and comprise a three terminal deviceincluding a source, drain, and gate. The terminals may be connected toother electronic elements through conductive materials, e.g., metals.The source and drain may be conductive and may comprise a heavily-doped,e.g., degenerate, semiconductor region. The source and drain may beseparated by a lightly-doped semiconductor region or channel. If thechannel is n-type (i.e., majority carriers are electrons), then the FETmay be referred to as a n-type FET. If the channel is p-type (i.e.,majority carriers are holes), then the FET may be referred to as ap-type FET. The channel may be capped by an insulating gate oxide. Thechannel conductivity may be controlled by applying a voltage to thegate. For example, applying a positive voltage or negative voltage to ann-type FET or a p-type FET, respectively, may result in the channelbecoming conductive. A transistor may be “on” or “activated” when avoltage greater than or equal to the transistor's threshold voltage isapplied to the transistor gate. The transistor may be “off” or“deactivated” when a voltage less than the transistor's thresholdvoltage is applied to the transistor gate.

The detailed description set forth above in connection with the appendeddrawings describes examples and does not represent the only examplesthat may be implemented or that are within the scope of the claims. Theterms “example” and “exemplary,” when used in this description, mean“serving as an example, instance, or illustration,” and not “preferred”or “advantageous over other examples.” The detailed description includesspecific details for the purpose of providing an understanding of thedescribed techniques. These techniques, however, may be practicedwithout these specific details. In some instances, well-known structuresand apparatuses are shown in block diagram form in order to avoidobscuring the concepts of the described examples.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and components described in connectionwith the disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), an ASIC, anFPGA or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, or any combination thereof designedto perform the functions described herein. A general-purpose processormay be a microprocessor, but in the alternative, the processor may beany conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor,multiple microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope and spirit of the disclosure and appended claims. For example,due to the nature of software, functions described above can beimplemented using software executed by a processor, hardware, firmware,hardwiring, or combinations of any of these. Features implementingfunctions may also be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations. As used herein, including in the claims,the term “and/or,” when used in a list of two or more items, means thatany one of the listed items can be employed by itself, or anycombination of two or more of the listed items can be employed. Forexample, if a composition is described as containing components A, B,and/or C, the composition can contain A alone; B alone; C alone; A and Bin combination; A and C in combination; B and C in combination; or A, B,and C in combination. Also, as used herein, including in the claims,“or” as used in a list of items (for example, a list of items prefacedby a phrase such as “at least one of” or “one or more of”) indicates adisjunctive list such that, for example, a list of “at least one of A,B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B andC).

Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation,computer-readable media can comprise RAM, ROM, EEPROM, flash memory,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such asinfrared, radio, and microwave, then the coaxial cable, fiber opticcable, twisted pair, DSL, or wireless technologies such as infrared,radio, and microwave are included in the definition of medium. Disk anddisc, as used herein, include compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above are also includedwithin the scope of computer-readable media.

The previous description of the disclosure is provided to enable aperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the scope of thedisclosure. Thus, the disclosure is not to be limited to the examplesand designs described herein but is to be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A method, comprising: selecting, for a memoryoperation, a memory cell comprising a memory element, the memory elementhaving a composition comprising: germanium in an amount ranging from 15atomic percent (at. %) to 35 at. % of the composition; antimony in anamount less than or equal to 50 at. % of the composition; tellurium inan amount greater than or equal to 40 at. % of the composition; and atleast one element selected from a group consisting of yttrium andscandium, in an amount ranging from 0.15 at. % to 10 at. % of thecomposition; and applying, during the memory operation, one or morevoltages to the memory cell.
 2. The method of claim 1, wherein the atleast one element selected from the group is yttrium.
 3. The method ofclaim 2, wherein the amount of yttrium is less than 5 at. % of thecomposition.
 4. The method of claim 1, wherein the amount of telluriumby atomic percent is greater than the amount of germanium by atomicpercent, is greater than the amount of antimony by atomic percent, andis greater than the amount of the at least one element by atomicpercent.
 5. The method of claim 1, wherein the amount of the at leastone element selected from the group consisting of yttrium and scandiumis less than 5 at. % of the composition.
 6. The method of claim 1,wherein the amount of germanium ranges from 15 at. % to 25 at. % of thecomposition.
 7. The method of claim 1, wherein the amount of antimonyranges from 10 at. % to 40 at. % of the composition.
 8. The method ofclaim 1, wherein the amount of tellurium ranges from 40 at. % to 65 at.% of the composition.
 9. The method of claim 1, wherein a bandgap of thecomposition ranges from 0.6 electronvolts to 0.9 electronvolts.
 10. Anapparatus, comprising: a first access line; a second access line; amemory cell comprising a memory element, wherein the first access lineis coupled with the second access line via the memory cell, and whereinthe memory element has a composition comprising: germanium in an amountranging from 15 atomic percent (at. %) to 35 at. % of the composition;antimony in an amount less than or equal to 50 at. % of the composition;tellurium in an amount greater than or equal to 40 at. % of thecomposition; and at least one element selected from a group consistingof yttrium and scandium, in an amount ranging from 0.15 at. % to 10 at.% of the composition; and a controller operable to cause the apparatusto: select the memory cell for a memory operation; and apply, during thememory operation, one or more voltages to the memory cell.
 11. Theapparatus of claim 10, wherein the at least one element selected fromthe group is yttrium.
 12. The apparatus of claim 11, wherein an amountof the yttrium is less than 5 at. % of the composition.
 13. Theapparatus of claim 10, wherein the amount of tellurium by atomic percentis greater than the amount of germanium by atomic percent, is greaterthan the amount of antimony by atomic percent, and is greater than theamount of the at least one element by atomic percent.
 14. The apparatusof claim 10, wherein the amount of the at least one element selectedfrom the group consisting of yttrium and scandium is less than 5 at. %of the composition.
 15. The apparatus of claim 10, wherein the at leastone element selected from the group is scandium.
 16. The apparatus ofclaim 10, wherein the memory cell further comprises a selector device.17. An apparatus, comprising: a selector device; a memory elementcoupled with the selector device, the memory element having acomposition comprising: germanium in an amount ranging from 15 at. % to35 at. % of the composition; antimony in an amount less than or equal to50 at. % of the composition; tellurium in an amount greater than orequal to 40 at. % of the composition; and at least one element selectedfrom a group consisting of yttrium and scandium in an amount rangingfrom 0.15 at. % to 10 at. % of the composition; and a controlleroperable to cause the apparatus to: select, for a memory operation, amemory cell comprising the memory element; and apply, during the memoryoperation, one or more voltages to the memory cell.
 18. The apparatus ofclaim 17, wherein the at least one element selected from the group isyttrium.
 19. The apparatus of claim 18, wherein the amount of theyttrium is less than 5 at. % of the composition.
 20. The apparatus ofclaim 17, wherein the amount of tellurium by atomic percent is greaterthan the amount of germanium by atomic percent, is greater than theamount of antimony by atomic percent, and is greater than the amount ofthe at least one element by atomic percent.